1. Field of the Invention
This invention relates to placement of wafer cassettes at the loading port of a process tool, and, in particular, to transfer of wafer cassettes to a loading port without lifting the cassettes from the vehicle.
2. Description of the Related Art
Semiconductor wafers or other such substrates are typically subjected to many processing steps that involve moving a cassette of wafers from one type of apparatus to another. For example, wafers that have been subjected to a process such as chemical vapor deposition may have to be moved to another apparatus to be cleaned and dried and then transferred to yet another apparatus for additional processing steps. It is very important that the wafers in process be kept isolated from contamination both during transfer between the process tool and the wafer cassette and during transport from tool to tool.
One wafer isolation technique involves transferring the wafers in a sealed cassette or FOUP (front-opening unified pod) and carrying the FOUP on a personally guided vehicle (PGV) or an automatically guided vehicle (AGV). At each location, it is necessary to open the sealed pod to remove the wafers and position them for processing. Preferably the FOUP has a front-opening door that can be opened by robotic equipment after the door frame has been sealed against the process equipment. Opening the FOUP robotically minimizes contamination and minimizes labor requirements.
Presently, when a PGV carrying a FOUP arrives at the front end of a process tool, a lifting device raises the FOUP and places it at the loading port of the process tool. The lifting device may be operated manually or automatically. This operation is cumbersome and slow and, in manual mode, requires substantial maneuvering on the part of the operator to align the FOUP precisely onto the loading port of the tool. Accidents sometimes occur wherein the FOUP is dropped during this lifting step.
The cost of processing semiconductor wafers, always a prime consideration, is often evaluated by the throughput per unit of cost. Another measure of cost is the throughput per area of floor space, wherein it is desirable to reduce the footprint of the apparatus employed. Related to both is the importance of reducing the capital cost of equipment. Advancements that can improve the competitive edge by either measure are highly desirable.
Preferred embodiments of the current invention describe an integrated wafer transport and transfer device, comprising a vehicle with an integrated docking platform, a wafer carrier on the docking platform, an elevator for the integrated docking platform to set the wafer carrier at a position suitable for loading wafers into a process tool, a latching mechanism to hold the vehicle in place and a horizontal movement control to adjust the position of the integrated docking platform on the vehicle. Preferably the wafer carrier is a FOUP (front opening unified pod), and the vehicle is a personally guided vehicle (PGV) or an automatically guided vehicle (AGV).
Either the docking platform holds the FOUP at the correct height or an elevator on the vehicle sets the docking platform at the correct height for sealing against a front face of a process tool. An automatic or a manual device can transfer the FOUP to seal against the process tool by moving the docking platform horizontally.
A method for processing wafers in a fabrication facility is described, which comprises storing the wafers in a wafer carrier or FOUP, carrying the wafer carrier on a vehicle wherein the wafer carrier is held on a docking platform at the height of the load port of a process tool, latching the vehicle to the process tool and moving the docking platform horizontally to seal the wafer carrier against a front face of the load port using a horizontal movement control integrated into the vehicle. One embodiment describes keeping a particular FOUP and a particular vehicle together as they move from one process tool to another.
A method of transferring wafers to a process tool is described that comprises carrying the wafers inside a FOUP on a cart, docking the cart at the process tool, sealing the FOUP to a load lock of the process tool without removing the FOUP from the cart and using a robot to transfer wafers between the FOUP and the process tool while the FOUP is still on the cart.